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BoffoRider

Casting flaws

11 posts in this topic

I have a buddy who is crazy with a dremel. He has ported and polished his 250 2 stroke and insists that there are many casting flaws left behind in all bikes. He claims that by cleaning up the casting flaws there would be a significant performance increase. He has already taken another guy's 426 and cleaned up the flaws and they both claim it would now easily match the power of my 450. Not that I necessarily believe them, but my questions are whether cleaning up these casting flaws would deliver a noticeable increase in power and are there really that many flaws left behind in these bikes? Any insight would be greatly appreciated.

Thanking you in advance,

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ABSOLUTELY! Will it help yes!Will it turn it into a fire breathing monster no!But every little bit helps right?But be careful be very careful a little boo boo and there goes

some $$$$$

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Is there anyone that has done this to their bike? What in particular should I be watching out for?

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Go to a pro. If you micro polish it has to be done on a machine. You cant do it by hand.

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If all he wants to do is remove the casting flaws thats fine, but dont let him do much more unless he has years of experience in this area...engine porting is a very delicate opperation that requires a professionals touch to make it perform properly. And for what its worth...the 426 does make just as much power as the 450...the 450 however, makes it a little more smoother and the bike is substantialy lighter.

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It will make a slight difference. Just make sure that he doesn't 'polish' the inlet ports. They need to remain rough.

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It will make a slight difference. Just make sure that he doesn't 'polish' the inlet ports. They need to remain rough.

Ditto, my understanding is that polishing the intake side might help with the very high top end, but not much good for anything else inbetween. The rough surface helps to mix the fuel and air. Now if you have some passages that just don't line up between bolt together pieces then that's a different story.

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Don´t let him play with your top!!!!!! :thumbsup:

You can´t do any porting without a flowbench. You will need that to mesure the vacum i the top. If wrong you will loose power instead of gaining.. As said earlier, you will need a pro to do it..

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another good point being is that if your friend messed it up ? whos payin for it ? and when a pro does it, atleast you know it will be done 100% right .. and with 100% percision

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i have a buddy who happens to be Casey Johnsons mechanic(#121 national)and even though casey rides a kx250,he has also worked on michael brandes 250 4 stroke.he told me that actually they dont touch the exhaust ports,they only massage the intake ports.believe it or not they try to make the opening smaller to increase velocity for increased throttle response and low to mid.when i tear mine down ill let him have at my head. :thumbsup:

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believe it or not they try to make the opening smaller to increase velocity for increased throttle response and low to mid.

This is true if the head design allows it. On some heads (426 for example) building up the port floor kills the flow at full valve lift, in which case you end up with a compramise. The 450 is much more suited to this procedure. You end up with higher port velocity for torque with no loss in flow. I've never heard of this being done on the exhaust port.... :thumbsup: normally you'd just use a stepped header pipe to get that effect.

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